Figure 3.

Whole-body indirect human calorimeter. A metabolic chamber for the measurement of substrate oxidation and energy expenditure over prolonged periods. In the airtight metabolic chamber (2.00 × 3.45 × 2.10 m; FHC-15S, Fuji Medical Science Co., Ltd., Chiba, Japan), air in the chamber was pumped out at a rate of 80 L/min. The temperature and relative humidity of the incoming fresh air was maintained at 25 °C and 55%, respectively. The chamber was furnished with an adjustable hospital bed, desk, chair, and toilet. Blood sampling and meal provision through the pass box did not affect the measurements. The concentrations of oxygen (O₂) and carbon dioxide (CO₂) in the outgoing air were measured with high precision by online process mass spectrometry (VG Prima PRO; Thermo Fisher Scientific, Winsford, UK). The precision of mass spectrometry, defined as the standard deviation of the continuous measurement of the calibrated gas mixture (O₂, 15%; CO₂, 5%), was <0.002% for O₂ and CO₂ [52]. O₂ consumption ($\stackrel{.}{\mathrm{V}}$O₂) and CO₂ production ($\stackrel{.}{\mathrm{V}}$CO₂) rates were calculated each minute, using an algorithm for improved transient response [53].